White Roofs to Cool your Building, your City and (this is new!) Cool the World

Transcription

1 White Roofs to Cool your Building, your City and (this is new!) Cool the World EESI Panel on Cool Roofs for Cooler Summers Capitol Visitor Center, 21 July 2011 Arthur H. Rosenfeld, Former Commissioner California Energy Commission. Distinguished Scientist Emeritus Lawrence Berkeley National Lab Presentation available at Filename EESI DC fm Blum Center from Russian Talk DR from EE Summit Sactp.. Path DinnerTalk Life at CEC. ARPA-E Summer in the city summer urban heat island 2 2 1

2 Bird s eye view of urban land use The surface of Sacramento, CA is about 20% roofs 30% vegetation 40% pavement Parking Area 12% Tree Cover 13% Grass 15% Barren Land 8% Sidewalk 5% Misc. 6% Roof 19% Road 22% Area by Land-Cover Category Above the Canopy 3 3 ~ 1 km 2 Reflective roofs stay cooler in the sun 50 Galvanized Steel Temperature Rise ( C) T Optical White Wh hite Paint White Cement Coat. IR Refl. Black Al Roof Coat. Lt. Gree en Paint Lt. Red Paint Red Clay Tile White Asphalt Shingle Green Asphalt Shingle Black Paint Solar Absorptance 2

3 White roofs, cool-colored roofs save money OLD NEW AC savings 15% flat, white AC savings 5% pitched, cool & colored AC savings 10% 5 pitched, white Chicago Heat Wave 1995, 739 Deaths The highest risk group lived on the top floors of buildings with black roofs 6 3

4 European Heat Wave 2003, 30,000 Deaths Moscow-Centered Heat Wave 2010,~10,000 Deaths 7 White roofs around the world 4

5 in Santorini, Greece 9 9 in Hyderabad, India and widely in the state of Gujarat, India

6 Walmart store in northern California, ~ Congratulations to UC Davis

7 White roofs are popular in Tucson, AZ Washington, DC (Federal) has problems

8 Pentagon Cooling our planet 8

9 Reference Book Consider a Spherical Cow (A Course in Environmental Problem Solving) By John Harte, UC Berkeley University Science Books, Mill Valley, CA 1988 Urban Heat Islands Ch3.B.9 17 Sunlight more than meets the eye Normaliz zed Solar Irradianc ce UV visible near-infrared Solar Irradiance Distribution 6.6% ultraviolet ( nm) 44.7% visible ( nm) 48.7% near-infrared ( nm) Air Mass 1 Global Horizontal (AM1GH) Solar Irradiance Wavelength (nm) 9

10 Atmospheric greenhouse effect (i/ii) Sun Earth 19 Absorption by the atmosphere. Solar reflective surfaces cool the globe via negative radiative forcing Source: Intergovernmental Panel on Climate Change (IPCC) 10

11 GLOBAL COOLING: making 100 m 2 (1000 ft 2 ) of gray roofing white offsets the emission of 10 t of CO How much CO 2 equivalent is offset if we whiten all eligible urban flat roofs worldwide? (i/ii) Answer: 24 Gigatonnes (Gt) 2/3 of a year s worldwide emission Gigatonne = billion metric tons If implemented over 20 years (the life of a roof or a program) this is 1.2 Gt/year

12 How much CO 2 equivalent is offset if we whiten all eligible urban flat roofs world-wide? (ii/ii) Offset is equivalent to taking 300 million cars off the road for 20 years. There are about 600 million passenger cars world wide, and they each emit 4 t CO 2 /year. 23 In terms of avoided power plants Full white roof potential can offset the emissions from 500 medium-sized coal fired power plants or 1,000 medium-sized gas fired power plants. That is just the albedo effect if the building is air conditioned, it will also avoid comparable real CO2 back at the power plant

13 3 papers and 1 memo estimate tonnes of CO 2 offset by 100 m 2 (1000 ft 2 ) of white roof. May 2010 Study (available at CoolWhitePlanet.org) Method Cloud cover estimation CO 2 offset (atmospheric) per 100 CO 2 offset (emitted) per 100 World-wide potential CO 2 offset (emitted) from m 2 ( ) m 2 cool roofs CO 2 offset compared to Akbari et al Akbari et al (LBNL) calculation ~ 50% 5.5 t 10 t 24 Gt 100% 2 Menon et al (LBNL) GCM + land use model (summer only) GCM 7 t 13 t 30 Gt 130% 3 Oleson et al (NCAR) [CO 2 values from private communication between Oleson & Menon] GCM + urban canyon model GCM 7 t 13 t 30 Gt 130% 4 VanCuren et al (CARB) measured solar radiation not needed 3 t 5 t Addresses CA only; coastal CA is foggy. 50% 25 It is assumed that of 1 tonne of CO 2 emitted only 0.55 tonnes remain in the atmosphere after one year, 25 so the atmospheric and emitted columns are just in the ratio of 0.55/1. Corroborations Since 2010 Vancuren, et al. is now refereed and published. Franco Cotana, et al., University of Perugia, will present their 2008 paper at Lawrence Berkeley National Laboratory (LBNL) on July 28 th, They estimate 7 tonnes per square meter vs. 10 by Akbari, et al. All estimates so far agree within a factor of 2. Now we need calculations for individual regions

14 27 Progress in energy efficiency standards In 2005, California s Title 24 energy efficiency standards prescribed white surfaces forlow sloped roofs on commercial buildings. Several hot states are following. Also New York City, effective January Vegetated ( green ) roofs are deemed white. In 2008, California prescribed cool colored surfaces for steep residential roofs in its 5 hottest out of 16 climate zones. Other U.S. states & all countries with hot summers should follow

15 Recent cool roof progress ( ) 2005 California Title 24 Flat roofs shall be white (15 out of 16 climate zones). Walmart adopts white roofs for ALL stores. EPA ENERGY STAR lists Cool Roof Materials 2010 June 1 st, 2010 Memo from U.S. Energy Secretary Steven Chu calls for all DOE Buildings to have white roofs, if cost-effective June 16 th, 2010 Marine Corp follows suit, Pentagon following slowly June 19 th, 2010 RetroFIT Philly announces winner of coolest block contest to white-coat black roofs of row houses Cool Cities launched see Spring 2011 US launched, at G20 Energy Ministers meeting, a voluntary Cool Roofs Working Group, and offered technical assistance to developing countries who join early. 29 To come 2012, 2013 Model codes will be modified to prescribe flat roofs shall be white ASHRAE for commercial buildings EECC for residential and commercial buildings But states and cities have to adopt model codes 30 15

16 Global Cool Cities Alliance could unite many initiatives and trade associations 31 What about Green (Vegetated) Roofs? ADVANTAGES In a rainy summer they cool buildings and cities comparably with white roofs. They hold up ~half of storm water.» DISADVANTAGES Their albedo is only ~20%,so they absorb sunshine, get warm, and then cool by evapo-transpiration. The absorbed heat is trapped by the greenhouse effect and the cooling by evaporation is cancelled within hours or days by the condensation of the water vapor into rain. For global cooling they are only one-third as effective as white roofs. Their first cost is ~$15/sq. ft. and may need an irrigation system. I support them, but, as a 5% niche, they are a distraction

17 Resources on the web Art Rosenfeld s website ArtRosenfeld.org Cool Colors Project CoolColors.LBL.gov Heat Island Group HeatIsland.LBL.gov Cool Communities Project CoolCommunities.LBL.gov i Roof Savings Calculator RoofCalc.com Global Cool Cities Alliance GlobalCoolCities.org Cool Roof Rating Council CoolRoofs.org Cool California CoolCalifornia.org EPA Heat Islands epa.gov/heatisland Energy Star Cool Roofs EnergyStar.gov 33 February